1. Field of the Invention
The present invention relates to a shifting mechanism for a gear change transmission and more specifically to a shifting mechanism for a gear change transmission where the shift forks are moved by a plurality of springs loaded by a plurality of ball screw actuators.
2. Description of the Prior Art
Gear change transmissions utilizing shift bar housing assemblies wherein one or more axially moveable shift bars, also known as shift rails and shift rods, each carrying or associated with a shift fork, are selectively axially moved to engage or disengage a selected transmission gear by axial movement of a clutch member, or of a gear carrying clutch teeth or of a jaw clutch, are well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 3,105,395; 3,283,613; 3,611,823; 4,152,949; 4,194,410; and 4,445,393; 4,754,665; 4,876,924; and 5,053,961, the disclosures of which are hereby incorporated by reference.
Non-operator actuated shift bar housing assemblies, usually actuated by pressurized hydraulic fluid, pressurized air, or electric motors and the controls therefor, are also well known in the prior art, as may be seen by reference to U.S. Pat Nos. 4,428,248; 4,445,393; 4,722,237 and 4,873,881, all assigned to the assignee of this invention and all hereby incorporated by reference.
While the prior art fluidly actuated shift bar housing assemblies are generally satisfactory and are presently widely utilized, usually for remotely controlled and/or automatically controlled change gear transmissions, the prior art assemblies were not totally satisfactory as they were complicated and/or expensive to produce, install and/or service. These prior art systems were also slow and difficult to control due to the compressibility of the air used to power the shift rails. The use of hydraulic fluid proved to be difficult due to leaks in the system which degraded performance and required extensive maintenance.